In ch. 8 of Rambam's Shmonah Prakim (Rambam's introduction to Pirkei Avot), he discusses free will. After maintaining that even the Egyptians had free will, despite Hashem telling Avraham that his descendants will be held in captivity and forced into slavery by a foreign nation, he explains that in the case of Hashem hardening the heart of Pharaoh, this was because Pharaoh had crossed the line of doing bad things out of his own free will and his punishment was to lose the ability to do tshuvah.
Then Rambam proceeds to bring evidence that Pharaoh did evil of his own free will:
"...as Scripture plainly states, (Exodus 1:9-10) "And he said unto his people, Behold, the people of the children of Israel is more numerous and mightier than we, come let us deal wisely with it". This they did through the dictates of their own free will and the evil passions of their hearts, without any external constraint forcing them thereto."
But this verse refers to the Pharaoh that first enslaved Yisrael, not the Pharaoh whom Hashem hardened his heart during the plagues! The first Pharaoh died. Why did the Rambam bring evidence from a different Pharaoh?